Bottom Rot of Lettuce

Bottom Rot is caused by Rhizoctonia solani and occurs wherever lettuce is grown on all types of lettuce. The disease is favored by warm, wet conditions and can cause severe losses in quality of heads. It occurs most frequently in plants at or near maturity.

Symptoms appear first on lower leaves in contact with the soil as small rust to brown spots, most often on leaf midribs. Bottom rot lesions are capable of rapid expansion and a soft, brown decay of lower leaves and crown occurs. Brown mycelium and amber droplets can be seen in infected tissues. Occasionally, a rot of the entire plant can develop. Rhizoctonia is a soil inhabitant that persists as mycelium or sclerotia in crop debris and other organic matter. The disease also occurs in greenhouse grown crops.

Management:

• Do not plant in fields having undecomposed residues from a previous crop.
• Deep plow to bury sclerotia.
• Practice crop rotation.
• Plant lettuce on raised beds.
• Improve soil drainage and avoid irrigation close to harvest.
• Select cultivars with an upright growth habit.
• Control weeds.
• Apply fungicides to the base of the plant including Quadris, Pristine, Flint, and Rovral.